1. Field of the Invention
This invention relates generally to surveying and geodetic measurements, and relates more particularly to a process and device for the automatic location of a reference marker, a receiver unit, a geodetic measuring device, and geodetic measurement systems.
2. Description of the Relevant Art
For a long time, there has existed the need, in connection with geodetic measurements, for automatically recognizing geodetic reference markers to be measured and located in the field, and, if possible, at the same time, obtaining a rough measurement. This necessity is even greater as a result of the tendency toward fully automatic integrated measuring systems.
Optical-electronic devices for the automatic location of geodetic reference markers or a retro reflector or a reflection foil are corresponding already used in various embodiments. Devices of this type thereby supplement the usual sensory measuring means usually employed in geodetic measuring work. The combination of a motorized theodolite with automatic marker detection provides substantial advantages.
Devices for finding markers and, therefore, also the present invention involve all measuring devices that are optically pointed to measuring points through directing means handled by humans.
The concept xe2x80x9cgeodetic measuring devicexe2x80x9d in this connection should generally be understood to be a measuring instrument that has devices for measuring or checking data with spatial references or also for pointing. Especially, this involves the measurement of distances and/or directions or the angles to a reference or measuring point. In addition, however, additional devices, for example, components for satellite-supported location determination (for example, GPS or GLONASS) may be present, which can be used for measurements in accordance with the invention. Here, geodetic measuring devices should be understood to mean theodolites, level or total stations, tachymeters with electronic angle measurements, and electronic optical distance measuring devices. Similarly, the device is suitable for use in specialized devices with similar functionality, for example, in military aiming circles or in industrial construction or process monitoring. These systems are thereby also included under the concept xe2x80x9cgeodetic measuring device.xe2x80x9d
Automated theodolites commonly used today, as an example of a geodetic measuring device, are not only equipped with angle and distance sensors, but also with an optical-electronic marker seeking positioning and marker point measuring device, hereinafter called automatic marker locating unit (AZE). Such theodolites are capable of moving directly to the marking point and measuring the spatial coordinates. When operating perfectly, the time saved with such automated instruments is substantial. If, in addition, the system can be operated through remote control, for example, from the marking point as a one-man station, then the work efficiency and the savings in cost achieved thereby is even greater.
An essential component of these automated measuring instruments is AZE. Various solutions are known, such as CCD or CMOS cameras with image processing, optical-electronic position-sensitive semiconductor detectors (PSD); 4-quadrant diodes, acoustical-optical beam scanners, etc.
The primary function of this AZE includes the exact measurement of a reference mark or a reflector precise to the millimeter, over short and long distances, where distances in excess of 1000 m can also be measured. In order to achieve this mm precision, the seeking devices have the disadvantage of a limited sensor site view field. Only in the case of small to medium view fields of a few degrees can point precisions of  less than 5 mm be achieved at 1000 m.
A substantial disadvantage of a small sensor view field is that the search for the marker is rendered more difficult, since the reference mark to be measured is often outside the view field at the beginning of a measurement. In many applications, especially in the short distance range, which does with a broad angle working field, an expanded sensor view field is advantageous.
Today, two methods are used in searching for markers. In one method, the sensor seeks the marker independently following a programmed algorithm or procedure; however, this takes time, due to the small field of view. In the second method, the search field is defined by the user, so that marker search proceeds in a more directed manner and takes less time; however, this has the disadvantage that the search field configuration must be reprogrammed every time the position changes.
A further disadvantage exists in following moved markers. In the case of tangential movements that are too rapid or jerky for the marker guidance of the automatic theodolite, it can occur that the marker leaves the view field of the marker detection device. Even a loss of the marker for a short time can then interfere with an efficient following process.
Further deficiencies in the case of devices with AZE in the state of technology are also the lack of robustness in the recognition of markers in the case of reflections by foreign markers. Foreign markers are those with a high degree of reflectivity, such as traffic signs. In marker recognition, the identification of the marker to be measured has not to date been satisfactorily solved, since especially the lack of robustness in solar reflections on objects with shiny surfaces has a disadvantageous effect.
While solar reflections on objects can be recognized with modern equipment, nevertheless the analysis necessary for this takes time, as a result of which the search process comes to a halt at every reflection.
In the case of rough-search sensors of the state of technology, due to the small sensor view field, the rough marker search requires too much time. The small view field, therefore, has effects that are out of proportion. In the first place, it has a smaller area of coverage of the environment, so that examining the search range requires a longer period of time. Secondly, the coverage must be done with a slower scan speed due to the shorter time that the object remains in the view field. A fan shape for the detection area of the sensors is, in this regard, more suitable, however the view fields, made up of fan angles of typically 1 to 5 degrees, is still much to small.
From the patent CH 676 042, a device is known with a fan-shaped transmitter and receiver, which is housed in a rotating measuring head. Light pulses are transmitted in a light fan from the transmitter unit; the reflected impulses are correspondingly evaluated with respect to angular information. However, this device has a substantial disadvantage of selecting not only the markers to be measured, but also outside interference objects. Such objects are, among other things, optically reflecting objects such as plate glass windows or traffic signs, and even sunlight reflected from motor vehicles.
An extension of the above marker search device for the rough determination of the marker coordinates is described in CH 676 041. In this case, a combination with an optical-electronic device is made for fine measurement. The actual marker search device sets up two fans that are perpendicular to each other, with which the location of the marker point is measured roughly. The subsequent fine measurement can then be carried out with the second device without the marker search procedure. The disadvantage of this combination is also the lack of robustness with respect to an erroneous locking in on foreign objects.
A further device is known from U.S. Pat. No. 6,046,800. A motorized theodolite, which is equipped with a sensor to detect the marker point coordinates, is revealed, consisting of one or two fan-shaped transmission bundles and two optical receiver channels. A special characteristic of this device consists of the fact that the optical axes of the transmitting channel and the two receivers lie triaxially in a single plane. This makes it possible to differentiate between normal reflecting and retro reflecting objects in a rotational or searching movement of the theodolite by evaluating the sequence over time of the two signals received. This method of pupil division on the receiver side, however, has the disadvantage that this differentiating characteristic exists only at short distances; in addition, the device is expensive, due to the two receiving channels.
From patent DE 196 23 060, a geodetic device for rough marker search is also known. This device consists of an optical-electronic vertical angle searcher essentially formed as a scanner. Transmitted and received beams are rotated around a (second) horizontally placed motor-driven axis. The intended result is a great range that is achieved on the basis of the parallel collimated optical bundles; this property is, however, purchased with the disadvantage of the point-type and therefore sequential and time consuming probing of the space. In the search process, the rapid vertically rotating sensor beam is simultaneously rotated slowly in the horizontal direction. A further disadvantage is the need for a supplementary angle measuring system on the scanner axis for the rough determination of the vertical angle. On the other hand, if the space were searched with a fan-shaped optical measuring bundle, then only a one-dimensional rotational movement around an axis would be necessary.
A substantial disadvantage of all previously known devices is the insufficient robustness against strongly reflecting foreign objects that can be mistakenly interpreted as marker objects, as well as interference with or at least the delay of the search process as a result of bright sunlight or reflections of the sun.
In most cases, the search process is supported manually through voice radio or data radio. In the device described in document DE 197 334 91, an additional optical receiving unit attached to the market object is used to check whether the search beam of the theodolite is hitting the marker object. If the corresponding search signal is being received, then the marker object reports its identification to the theodolite using data radio. This solution, while robust, affects the ergonomics at the marker object.
The problems to be solved by this invention consist of an improvement of the sensor devices defined above.
In this regard, one problem consists of providing a geodetic measuring device for the rough search of the marker, which is suitable for locating and identifying, as rapidly as possible, marker objects and determining rough coordinates, and which has a shorter searching time with a range of up to 1000 m. The speed of the search for the marker is a main problem, since it demands a large sensor viewing field, which can be achieved by a corresponding wide fan angle. As fan angles become larger, however, the range decreases. The problem to be solved by the invention is therefore to achieve the range of geodetic applications and simultaneously a high search speed.
A further problem consists of making possible a search process that is robust against foreign light and self-reflection at foreign markers. The search process, at the same time, cannot be delayed or interrupted by foreign markers with a high degree of reflection or by items with solar reflections. At the same time, the problem includes the simultaneous identification of the marker objects to be measured on the basis of suitable identification characteristics, even during the search process.
These problems are solved in accordance with the present invention. This invention substantially concerns an optical-electronic marker search device consisting of a fan-shaped transmitting channel that irradiates the marker to be located, a fan-shaped receiving channel that receives light reflected from the marker object, a motorized measuring device, for example, a theodolite, which moves around one of the two axes during the search process, at least one electronic evaluating unit to determine the rough location of the marker point, signal strength of the reflected signal, the width of the marker object in the scanning direction, and the distance to the marker object. Optically, the duration of the reflected optical signal can also be determined.
Both the planes of the two optical-electronic light fans and the axis of rotation of the theodolite (=scanning axis for the search procedure) are oriented parallel to each other. In the following, the concepts of the horizontal and vertical motion are to be understood in such a manner that the corresponding components and a corresponding movement are present in a movement. A horizontal movement of the transmitter unit can therefore especially also be achieved by a movement tilted toward the horizon.
A powerful and sensorily sensitive running time measuring device serves as a marker search device. Suitable running time meters with pulse modulation have a great range and a short measuring time. The attainable optical transmission powered with pulse laser diodes only millimeters in size is over 100 Watts. This makes it possible to achieve the range required for geodetic applications even with fan-shaped spreading of the transmitted beam. During a search run, the running time meter is operated in the continuously measuring mode. In this regard, the transmitter sends out optical impulses at a rate in the kHz range. Since the device is run in the single-shot evaluation process, information concerning the scanned environment is available in the nanosecond to microsecond range. The pulses received are probed with a rapid AD converter, which provides an intensity image of the environment. At the same time, the pulses probed can, for example, be stored in a 2D memory and evaluated later or a first analysis may be made soon and the further evaluation based on these first results which, for example, can be a bringing together or concatenation of the pulses.
The dimensioning of the optical transmitting fan is done in such a manner that it covers the environment typically to be measured in the vertical direction. The divergence in the direction perpendicular to the fan is preferably narrow, limited by diffraction.
A search with a device in accordance with the invention provides, as an output, an intensity image of the environment searched. The two-dimensional intensity image can be evaluated after the scan is completed or even simultaneously or soon after the recording. Possible results of such an evaluation can be, for example intensity maxima of any marker objects, a time for finding the marker or the equivalent angles to the marker object, or the distance to the marker object.
The robustness vis-à-vis solar reflecting surfaces and reflecting distant markers is improved or attained only by using the invention. Due to the strong laser pulse, solar reflecting surfaces are not visible in the two-dimension intensity image for two reasons. First of all, the laser radiation of the transmitters is of a narrow spectrum and a comparatively narrow interference filter in the reception process blocks the sunlight to a great extent. Secondly, the pulse lasers generate strong light flashes whose density of radiation is greater than that of solar reflections. Robustness against solar reflective surfaces is thereby achieved.
The necessary robustness against foreign or interference markers is more difficult to achieve. At first, in the two-dimensional intensity image, in addition to the actual marker object to be located, there often appear further optically reflecting objects.
In the near range under 10 m, the problem can be solved by a special biaxial arrangement of the two optical fans. Transmitter and receiver are biaxially next to each other, where the sideward displacement is perpendicular to the fans. The view fields of the transmitter and receiver do not overlap below 10 m as a result. Single reflecting objects, such as mirrors, are not seen in this distance range by the receiver, only retro reflecting marker objects with a sideward displacement of the reflected beam such as, for example, the triple prisms common to measuring work generate a measurable received signal. As a result of this, the robustness below 10 m is solved by the biaxial arrangement.
At all other distances, the real marker objects must be identified from the objects included in the two-dimensional intensity image in accordance with the invention.
Any marker object generates both a characteristic signal process and a characteristic width as a function of the distance. The identification of marker objects is therefore possible using two distance-related measurement curves. For the object distance measured in each case, the width of the object and the signal strength are checked to determine whether they are within the tolerance range of the marker object sought. Depending on concrete marking parameters and measuring conditions, it may be sufficient to perform only a comparison with respect to a limit value, for example, a comparison with the lower limit value with respect to the signal and with the upper limit value with respect to the object size.
If, during a scan, a reflected object is irradiated, then the signal and the object width are continuously compared to the tolerance values loaded. As soon as the transmitter fan has completely covered an object and all measured values lie within the tolerance limits, a marker object is identified and found. Depending upon application, the search process is stopped at the point or the coordinates, optionally along with parameters such as signal and width, are stored and the search process is continued without interrupting the scan so that further marker objects can be sought and found.
The case, which is entirely possible, that at certain fan settings multiple marker objects occur simultaneously at different distances can be handled without a problem on the basis of distance measurements.
In many applications, immediately after the instrument setup, the entire environment is scanned. This generates a two-dimensional intensity image, which contains all strongly reflecting objects. The coordinates of the irrelevant market objects, such as interference and foreign markers, are calculated and stored. With the knowledge of the coordinates of all interfering objects and foreign markers, these can be blocked out of further search runs. As a result, this makes it possible to save additional searching time, since the objects irrelevant to the measuring task no longer exist from a sensory point of view.
When a marker object is found, the distance and one direction coordinate are known. Next, the second spatial direction is measured. This is achieved according to the known search procedure with the automated marker locating unit (AZE) present in the theodolite. The AZE search and measurement procedure is very efficient and rapid in this case, since only 1-dimensional movement or travel is necessary. The combination of the two devices results in a further advantage. Since the AZE measures the position of the marker object precisely to angular seconds, at the end of the AZE search and measurement process the marker point coordinates are known not only roughly, but with geodetic precision in the millimeter to sub-millimeter range.
The combination of the marker search device with an automatic marker locating unit (AZE), in accordance with the present invention, makes possible the complete and mm-precise determination of the 3D coordinates of marker objects.
An essential property of the process and the device in accordance with the invention is the speed of the search process. A complicating factor lies in the large signal dynamic resulting from the geodetic distance range.
In a device according to the invention, this problem is supported or solved by measures taken on the transmitter side. The high signal dynamic can be allowed for by transmitting multiple laser pulses of differing intensity. The signal dynamic is thereby divided onto transmitter and receiver. In the short-distance range, the receiver evaluates the weak pulses with lower amplitude in the long-distance range, the strong pulses with higher amplitude.
A suitable application of the device in accordance with the invention is represented by modular integration in a motorized theodolite with automatic marker locating unit (AZE) according to patent U.S. Pat. No. 6,031,606.
The process according to the invention as well as a device according to the invention and a geodetic measuring device according to the invention are described in greater detail in the following, on the basis of the sample embodiments schematically represented in the drawing, purely as an example.
The features and advantages described in the specification are not all inclusive, and particularly, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification and claims hereof. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter, resort to the claims being necessary to determine such inventive subject matter.